The present invention relates to a biological aerosol filtration assembly, cartridge and system and particularly, but not exclusively to a biological aerosol filtration assembly for filtering viruses and bacteria from gaseous matter, such as exhaled air.

Continuous positive airway pressure therapy or "CPAP" therapy is a known technique for assisting individuals who have breathing problems, such as sleep apnea. The technique involves the supply of a mild air pressure throughout the breathing cycle of an individual, to keep the individual's airways open and unobstructed. The mildly pressurized air is provided to the individual via a tube which is connected at one end to a flow generator for regulating the flow of air, and at the other end to a face mask that is typically secured around the mouth and nose of the individual. The mask further comprises a one-way valve so that during the exhalation phase of the breathing cycle, the exhaled air can pass out from the mask to the surrounding environment.

CPAP devices are used for individuals which have difficulty breathing, however, for those individuals who are unable to breathe, ventilators or respirators are used to mechanically move breathable air into and out from the lungs of the individual. These ventilators typically comprise an air reservoir, and a set of valves and tubes for delivering the air from the reservoir to the individual. Once the individuals' lungs have inflated and the air pressure applied by the ventilator is removed, the elasticity of the lungs will typically cause the lungs to collapse and thus expel air therefrom, via a one way valve, typically to the surrounding environment.

However, in both of the above examples, the exhaled air may comprise viruses and bacteria which can be subsequently inhaled by persons in the surrounding environment and as such, otherwise healthy individuals have the potential to become infected by inhaling air laden with these exhaled viruses and bacteria.

W02005/060366 discloses a filtration device integrated into a face mask that may be worn by a user. The filtration device utilizes an ionisation technique and an electrostatic field to remove dust, pollens bacteria and viruses. However, this device offers a limited interaction of the particulate laden air with the electrostatic field owing to the compact form of the mask (and thus limited surface area upon which to precipitate the particulate matter) and the speed with which air passes through the mask. The device is thus only partially effective at removing the desired particulates from the air. In addition, the restricted air flow through the mask owing to the presence of the louvres and intersecting electrode fins can exacerbate the breathing difficulty experienced by certain users. We have devised a biological air filtration assembly which alleviates at least some of the above-mentioned problems.

In accordance with the present invention, there is provided a biological aerosol filtration assembly, the assembly comprising: a separation chamber having an inlet for receiving biologically laden aerosol into the separation chamber and an outlet via which cleaned aerosol may leave the separation chamber, the separation chamber defining an aerosol flow path between the inlet and the outlet thereof; at least one first electrode and at least one second electrode; the at least one first and at least one second electrode being disposed in spaced relation within the separation chamber, the at least one first electrode being connectable to a first pole of an electrical power supply and the at least one second electrode being connectable to a second pole of the electrical power supply; wherein the at least one first electrode comprises an ion emission zone which is configured to emit a stream of charged particles into the separation chamber to electrostatically charge the biologically laden aerosol to cause biological material within the aerosol to electrostatically precipitate upon the at least one second electrode; and wherein the assembly further comprises means for regulating an air flow speed through the separation chamber.

The means for regulating the air flow speed ensures that a peak air flow speed through the separation chamber remains below a threshold, to provide for a suitable interaction of biologically laden aerosol, such as exhaled air, with the charged particles generated by the first electrode, and thus an increased precipitation efficiency of the biological matter onto the second electrode.

In an embodiment, the at least one first electrode is disposed proximate the inlet of the separation chamber. This is to encourage the ionisation of the biologically laden aerosol as it enters the chamber, and thus provide a greater distance in the direction of the general flow of air for aerosol particulates to be electrostatically attracted onto the surface of the second electrode. A succession of first electrodes in the path of the general flow of air provides an increased range/distance over which the biologically laden aerosol becomes ionized and so increases the overall fraction of the aerosol particulates precipitated onto the second electrode. In this respect, the at least one first and second electrodes may be disposed at non-overlapping longitudinal regions of the separation chamber. However, in an alternative embodiment, it is envisaged that the at least one first and second electrode may instead extend at overlapping longitudinal regions of the separation chamber, and in yet a further alternative, a second electrode of the at least one second electrode may be disposed upstream of the at least one first electrode.

In an embodiment, the ion emission zone may comprise a fibrous or sharpened zone of the at least one first electrode.

In an embodiment, the at least one second electrode is disposed proximate the outlet of the separation chamber.

In an embodiment, the at least one second electrode is disposed between the inlet and outlet of the separation chamber, within a flow path of aerosol through the separation chamber. The at least one second electrode comprises an increased surface area compared with the ionisation zone for providing a larger trapping area over which the biological material within the aerosol flow may deposit or otherwise become trapped thereon. In an embodiment, the second electrode presents a convoluted flow path for the aerosol in passing along the aerosol flow path to encourage the biological material within the aerosol to electrostatically precipitate onto the second electrode. In an embodiment, the at least one second electrode comprises a wire mesh or apertured member, such as an apertured plate or cylinder. Alternatively, or in addition thereto, the at least one second electrode may comprise or further comprise an electrically conductive porous body or a fibrous body, such as a ball of copper wire wool. In a further embodiment, the second electrode may comprise a liquid electrode disposed within a reservoir within the separation chamber.

In an embodiment, the at least one second electrode comprises a viricidal or anti-microbial coating, such as titanium dioxide or silver, sufficiently conductive to provide an electrically attractive surface for precipitation of the biologically laden aerosol.

In an embodiment, the means for regulating the air flow speed through the separation chamber comprises a buffer chamber, which is disposed upstream of the separation chamber, for receiving the biologically laden aerosol prior to entering the separation chamber. The buffer chamber may comprise flexible and/or distendable side walls to permit a volume of the buffer chamber to vary with the breathing cycle of a user. For example, the buffer chamber may comprise a chamber having elastomeric side walls, or simply a bag. The buffer chamber is arranged to reduce the peak air flow rate through the separation chamber without substantially increasing the resistance to the flow through the assembly and specifically without increasing a resistance to the air flow out from a CPAP mask. In this respect, the means for regulating the aerosol flow speed is designed to make the assembly compatible with the outflow of exhaled air from CPAP masks and ventilators. In an embodiment, the buffer chamber comprises a larger volume than the separation chamber.

In an alternative embodiment, the means for regulating the air flow speed is arranged to minimize the increase in resistance to the air flow out from a CPAP mask,. In this respect, the separation chamber may comprises or further comprises an increased cross-sectional area of the outlet of the separation chamber relative to a cross-sectional area of the inlet to the separation chamber. The larger outlet is arranged to reduce the pressure of the aerosol towards the outlet of the separation chamber and thus reduce the aerosol flow speed towards the outlet of the separation chamber.

There is an advantage gained from a comparatively reduced cross-sectional area towards the inlet compared with the outlet, and in particular regions including the at least one first electrode, resulting in an increased efficiency of electrostatic ionisation of aerosol due to improved average dwell time of the particulates in the aerosol proximate the first electrode.

In a further embodiment, the means for regulating the air flow speed comprises a pump or impeller.

It is known that air exhaled from individuals comprises a moisture content, namely water vapor, and as the temperature of the biologically laden aerosol falls from body temperature towards room temperature, the water vapor will condense into aerosol droplets and this moisture can accumulate upon the interior surfaces of the separation (and buffer) chamber and the first and second electrodes over a period of time. This accumulation on the first electrode can degrade the performance of electrostatic precipitation by smoothing the surface of the electrode thereby reducing the peak electric field strength required for ionisation at the first electrode. The condensation of water vapor onto collection surfaces decreases the remaining suspended mass of aerosol particulates to be electrostatically precipitated, thereby reducing the level of the applied electrical current required to cause precipitation of the biologically laden component of the remaining aerosol.

Moreover, excessive build-up of moisture on surfaces of the separation chamber can result in electrical pathways developing between the first and second electrodes which effectively reduce the potential difference between the electrodes and in certain situations can lead to a direct electrical short. In an embodiment, the assembly further comprises a moisture absorbing coating, such as silica gel, disposed upon an interior of the separation and/or the buffer chamber. The moisture absorbing coating may be separated from the interior of the respective chamber by a porous lining or membrane. In a further embodiment, it is envisaged that the lining or coating may comprise a colour changing chemical to indicate when the moisture absorbing capacity has been reached, and thus indicating that the assembly requires replacement. In an embodiment, the separation chamber further comprises moisture/condensate traps disposed along an interior surface thereof for minimising any tracking of moisture/condensate along the interior surface of the separation chamber. Moisture/condensate within the separation chamber is preferably collected in a sump.

In a further embodiment, the assembly comprises a cooling unit for cooling the biologically laden aerosol, the cooling unit being disposed upstream of the separation chamber. The cooling unit is arranged to cool the air to effectively reduce the water vapor content of the air by condensing the water onto cooled condensing surfaces in contact with the air. Such condensate may entrain some fraction of the biological aerosol. In an embodiment, condensing surfaces of the cooling unit comprise a viricidal or anti-microbial coating, such as titanium dioxide or silver. In a further embodiment, the condensing surfaces of the cooling unit comprise a liquid viricidal or anti-microbial solution. In this embodiments, after passing through the cooling unit, the air is heated to approximately ambient room temperature to ensure that subsequent sections of the biological aerosol filtration assembly process substantially dry air at a temperature significantly above the new dew point of the dried air.

In a further embodiment, the assembly comprises a heating unit for heating the biologically laden aerosol, the heating unit being disposed upstream of the separation chamber. The heating unit is arranged to heat the aerosol to effectively reduce the water droplet content within the aerosol. The condensing cooling unit and a subsequent heating unit may be combined to form an integrated cooling and heating unit to ensure that water condensation does not occur inside the separation chamber due to the dew point of the aerosol being reached.

In an embodiment, the assembly further comprises a connector for fluidly coupling with an outlet of a CPAP mask. The connector may be arranged to fluidly couple with a hose for communicating the biologically laden aerosol from the CPAP mask to the filtration assembly.

In an embodiment, the outlet of the separation chamber comprises a protective gauze or mesh disposed thereacross to prevent access to the interior of the chamber and thus unintentional contact with the first and/or second electrodes.

In an embodiment, the assembly further comprises at least one ultra violet radiation generating source which is arranged to irradiate an interior of the assembly, such as an interior of the separation chamber and/or the buffer chamber, with ultraviolet radiation to assist in the sterilization of the biologically laden aerosol. The ultra violet radiation generating source may comprise a light emitting diode (LED) for emitting ultraviolet radiation. In an embodiment, the assembly further comprises a first and second closure for sealingly closing the interior of the separation chamber, such as via a hermetic seal, to prevent any egress of material therefrom. Such a sealing closure might be deployed at the end of use of the filter.

In accordance with a second aspect of the present invention there is provided a biological aerosol filtration cartridge comprising an inlet for receiving biologically laden aerosol into the cartridge and an outlet via which cleaned aerosol may exit the cartridge, the cartridge further comprising a flow path for aerosol between the inlet and the outlet of the cartridge, the cartridge further comprising a biological aerosol filtration assembly according to the first aspect fluidly coupled within the flow path.

In accordance with a third aspect of the present invention there is provided a biological aerosol filtration system comprising a filtration assembly according to the first aspect and an electrical power supply comprising a first and second electrical pole.

In accordance with a fourth aspect of the present invention there is provided a biological aerosol filtration system comprising an aerosol filtration cartridge according to the second aspect and an electrical power supply comprising a first and second pole.

Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 is schematic illustration of a biological aerosol filtration cartridge according to an embodiment of the present invention comprising a biological aerosol filtration assembly according to a first embodiment of the present invention;

Figure la is a magnified view of the integrated cooling and heating unit illustrated in figure 1;

Figure 2 is a schematic illustration of a biological aerosol filtration cartridge according to an embodiment of the present invention comprising a biological aerosol filtration assembly according to a second embodiment of the present invention; and,

Figure 3 is a schematic illustration of a biological aerosol filtration system according to an embodiment of the present invention.

Referring to figure 1 of the drawings there is provided a biological aerosol filtration assembly 10 according to a first embodiment of the present invention for separating bacteria and viruses from an air flow, such as air exhaled from an individual. Flowever, it is to be appreciated that the assembly 10 may be used to filter bacteria and viruses from other air flows, including for example, air circulating in air conditioning units. In this specification, the term "aerosol" is understood to include the suspension of fine solid and liquid particles, such as viruses, bacteria, pollen, allergens, dust, saliva and phlegm and other bodily fluids, within a gas, such as exhaled air and air flowing within air conditioning systems. However, for simplicity the following description will refer to the specific example of exhaled air as the aerosol.

The assembly 10 is designed to be coupled with an output of a CPAP mask or ventilator (see figure 3 of the drawings), and as such, is designed to present a minimal resistance to the outflow of exhaled air from the mask or ventilator to avoid interrupting the breathing cycle of the individual. Moreover, the assembly 10 is configured to be replaceable following a period of use, and as such is disposed within a disposable cartridge 50.

The cartridge 50 may comprise an injection-moulded or machined unit formed of a rigid plastics material for example and comprises an inlet 51 for receiving the biologically laden aerosol, such as exhaled air, into the cartridge 50 and an outlet 52 via which cleaned air may exit the cartridge 50. The air flow is arranged to pass from the inlet 51 to the outlet 52 along a flow path 53 comprising a separation chamber 20 within which the biological matter within the exhaled air is removed from the air flow. The separation chamber 20 comprises an inlet 21 arranged in fluid communication with the inlet 51 to the cartridge 50, and an outlet 22 disposed in fluid communication with the outlet 52 of the cartridge 50.

The separation chamber 20 further comprises at least one first electrode 23 which extends into the chamber, such as through a side wall 20c thereof or through an end wall 20a. The first electrode 23 comprises an electrically conductive rod or wire which extends through an electrically insulating sheath or cover (not shown). A proximal end of the first electrode 23 is electrically coupled with an electrical connector 24 disposed on the separation chamber 20 or exterior of the cartridge 50, for electrically coupling with a first pole (such as a negative pole) of a high voltage DC electrical power supply (see figure 3 of the drawings). A distal end of the first electrode 23 is disposed within the chamber 20 and comprises an electrically exposed ion emission zone 23a for facilitating the release of charged particles, namely electrons, therefrom, for electrostatically charging the biologically laden aerosol. The ion emission zone 23a is disposed proximate the inlet 21 of the chamber 20 and may comprise a sharpened or fibrous zone, having vertices, edges or points which can serve as ion emitters. In the illustrated embodiment, the ion emission zone is directed along the separation chamber toward a second electrode, however, it is to be appreciated that the first electrode 23 may alternatively extend across the separation chamber, at an acute angle to a longitudinal axis thereof. The first electrode 23 further comprises a collar or hemispherical shield 25 disposed thereon which is positioned between the inlet 21 and the ion emission zone 23a, so that the ion emission zone 23a is disposed at the leeward side of the aerosol flow. This configuration serves to minimize any detritus or moisture within the air flow from depositing upon the ion emission zone 23a. However, in yet a further embodiment which is not illustrated, the first electrode 23 may comprise or further comprise an annular ring located within the inlet 21 to the chamber 20 and having a plurality of ion emission zones.

The separation chamber 20 further comprises a second electrode 26 which in the illustrated embodiment is disposed proximate the outlet 22 of the chamber 20. However, the second electrode 26 may alternatively be disposed at the same longitudinal distance along the chamber 20 as the first electrode 23 (or even upstream of the first electrode 23). The second electrode 26 comprises an electrically conductive porous or fibrous body, such as a body of copper wire (namely, wire wool), or one or more electrically conductive meshes or gauzes (see figure 2 of the drawings). The second electrode is electrically coupled with an electrical connector 27 disposed on the separation chamber 20, or an exterior of the cartridge 50, for electrically coupling with a second pole (such as a positive or grounded pole) of a high voltage DC electrical power supply (see figure 3 of the drawings). The second electrode 26 serves to collect biological material thereon via electrostatic precipitation and thus comprises a large surface area for trapping the biological material. Moreover, to sterilize or otherwise kill any bacteria or viruses which deposit on the second electrode 26, the second electrode 26 may be coated with a viricidal coating (not shown), such as titanium dioxide or silver.

The assembly 10 further comprises means 90 for regulating the speed of exhaled air through the separation chamber 20, while at the same time presenting a minimal resistance to the outflow of exhaled air from the CPAP mask. This means 90 is important so that the air flow speed and particularly the peak air flow speed along the separation chamber 20 remains below a threshold speed so that the exhaled air has sufficient time to interact with the electrons (not shown) generated by the first electrode 23 and thus become electrostatically charged. The means 90 for regulating the air flow also ensures that the electrostatically charged species including viruses and bacteria within the air flow have sufficient time to interact with the second electrode 26 and thus electrostatically precipitate from the air flow onto the second electrode 26.

The means for regulating the air flow speed may comprise a pump or impeller (not shown). However, in the first embodiment illustrated in figure 1 of the drawings, the means 90 for regulating the air flow speed comprises a relative sizing of the inlet 21 and outlet 22 to the separation chamber 20. Specifically, the inlet 21 to the separation chamber 20 comprises a reduced cross-sectional area compared with the outlet 22 such that aerosol passing into the chamber 20 through the inlet 21 experiences a reduced air pressure, which causes the flow of aerosol to slow on entering the chamber 20. The separation chamber 20 comprises a substantially frusto-conical shape, (although the skilled reader will recognize that the chamber 20 may be shaped differently) and the inlet 21 comprises an opening in the first end wall 20a of the chamber 20, namely the end wall comprising the reduced cross-sectional area, and the outlet 22 is disposed on the opposing second end wall 20b, namely the end wall having the greater cross-sectional area.

The separation chamber 20 further comprises a moisture absorbing coating 28, such as silica gel, disposed along an interior of the curved side wall 20c thereof, which is separated from the interior of the chamber 20 by a permeable layer 29. The coating 28 is arranged to absorb any moisture within the air flow to minimize the build-up of any moisture on the first and second electrodes 23, 26. An accumulation of moisture upon the interior of the separation chamber 20 and within the composition of the biologically laden aerosol can reduce the impedance between the first and second electrodes 23, 26 and thus reduce the ionisation potential of the ion emission zone 23a to generate electrons. The accumulation of moisture over the surface of the ion emission zone 23a of the first electrode 23 can also reduce the generation of electrons at a given potential between the first and second electrodes. In addition, the accumulation of moisture on electrically insulating surfaces can lead to the development of electrical pathways between the first and second electrode 23, 26 which can result in an undesirable and potentially damaging electrical short between the electrodes 23, 26. Accordingly, the moisture absorbing coating 28 may further comprise a colour changing chemical (not shown), such as cobalt chloride, which is arranged to change colour when the moisture absorbing capacity of the coating 28 has been reached, thereby providing a visual indication of the requirement to replace the separation chamber 20.

In order to minimize any tracking of moisture or condensate along the interior curved surface 20c of the chamber 20 toward the proximal end thereof, and thus toward the first electrode 23, the separation chamber 20 may further comprise moisture/condensate traps 20d, which may comprise annular projections which extend radially inward of the chamber 20, from the interior surface 20c thereof. These traps 20d serve to disrupt the flow of moisture/condensate along the interior surface 20c of the chamber 20 and act as sites via which moisture/condensate can accumulate and fall to a lower region of the chamber 20 and become collected within a sump S. Moisture/condensate within sump S can subsequently be drained to a vessel (not shown) for disposal via a drain valve V.

In a further endeavor to reduce the moisture within the air flow, the assembly 10 may further comprise a cooling or chiller unit 30 disposed upstream of the separation chamber 20, within the air flow path 53. The cooling unit 30 may be disposed within cartridge 50 or fluidly couplable therewith. The cooling unit 30 is fluidly with the separation chamber 20 and is arranged to absorb heat from the air flow to cause water vapor to condense from the air flow. Air exhaled at 37°C at 100% humidity contains approximately 43.9g/m ³ water as vapor. At 21°C this vapor-holding capacity drops to approximately 18.3g/m ³ water. Accordingly, by reducing the temperature of the aerosol it is possible to reduce the water content through condensation and this condensation may be collected in a collection chamber comprising a biocide/viricide. The cooler unit 30 may comprise a heat exchanger comprising a coil of ducting (not shown) thermally coupled to a finned metal structure that is disposed within the aerosol flow, and through which the aerosol is arranged to flow. The ducting is arranged to circulate a fluid for extracting the heat from the finned metal structure to maintain the cooling ability of the finned metal structure.

Cooled air exiting the cooler unit 30 will comprise water droplets entrained within the air flow. Accordingly, to maintain the air above its dew point, the cooled air is preferably heated prior to passing into the separation chamber 20. In this respect the assembly further comprises a heater unit 40 fluidly coupled with the cooler unit 30.

The heating unit 40 may comprise a heating element or wire (not shown) for Ohmic heating of the aerosol to reduce the moisture content. In this respect, the heating unit 40 may similarly comprise electrical connectors (not shown) disposed on an exterior of the assembly 10, or an exterior of the cartridge 50 for electrical coupling with an electrical power source (not shown).

However, in a preferred embodiment, as illustrated in figure 1, the heat extracted by the cooler unit 30 is preferably arranged to heat the air flow downstream thereof via a heating unit 40, to re-warm the air and convert the entrained water droplets to water vapor. In this respect, the cooler unit 30 and heating unit 40 may be integrated and the cooling and heating may be achieved using a Peltier device. The integrated cooling and heating unit is illustrated in more detail in figure la of the drawings and comprises a flow duct F having an inlet 31 and an outlet 42, and a substantially planar, Peltier device P which extends across the duct F and which is orientated substantially perpendicular to the air flow. The Peltier device P is arranged to effectively block the flow of air along the flow duct and as such, the integrated unit further comprises a bypass chamber C which extends between a first and second opening disposed in a side wall of the flow duct, namely an outlet 32of the cooling unit 30 and an inlet 41 of the heating unit 40, either side of the Peltier device P. In this respect, air passing into the flow duct F must pass along the bypass chamber C to move downstream of the Peltier device P within the flow duct.

The Peltier device P comprises a cooling surface 33 which faces the inlet 31 to the flow duct and a heating surface 43 which faces the outlet 42 of the flow duct F. The integrated unit further comprises a first array of metal fins 34 arranged in thermal contact with the cooling surface 33 which extends along the flow duct F from the cooling surface 33 beyond the outlet 32 of the cooling unit 30 toward the inlet 31 to the duct F, and a second array of metal fins 44 arranged in thermal contact with the heating surface 43 which extends along the flow duct F from the heating surface 43 beyond the inlet 41 to the heating unit 40, toward the outlet 42 of the flow duct. Accordingly, air passing along the flow duct F from the inlet 31 is arranged to thermally interact and thus exchange heat with the first array of metal fins 34 before passing into the bypass chamber C. After passing into the chamber C, the cooled air is arranged to pass back into the flow duct F via the inlet 41 to the heating unit 40 and thermally interact and exchange heat with the second array of metal fins 44 before passing to the outlet 42 of the flow duct F. The condensate which forms on the first array of metal fins is arranged to drain into the bypass chamber C via the outlet 32 and this condensate may be further drained into a collection chamber (not shown) via a drain valve V formed in a base of the bypass chamber C.

The Peltier device is electrically coupled to an electrical power supply (not shown) via electrical connections 35, 45 disposed on an exterior of the cooling and heating unit 30, 40, or the cartridge 50 when integrated therewith. When powered, a temperature differential is created between the cooling surface 33 and the heating surface 43 in dependence of the electrical current supplied to the device P. In this respect, the cooling of the incoming air and the heating of the outgoing air can be controlled by controlling the electrical supply to the Peltier device P.

Referring to figure 2 of the drawings there is illustrated a biological aerosol filtration assembly according to a second embodiment of the present invention disposed within a biological air filtration cartridge 150. The filtration assembly 110 of the second embodiment comprises substantially the same components as the filtration assembly 10 of the first embodiment and as such, similar components have been referenced with the same numerals but increased by 100. Flowever, the filtration assembly 110 of the second embodiment differs from the filtration assembly 10 of the first embodiment by virtue of the means 190 for regulating the air flow speed through the separation chamber 120. Additionally, the filtration assembly 110 of the second embodiment comprises an alternative configuration for the separation chamber 120 and second electrode 126, although this configuration could equally be used with the filtration assembly 10 of the first embodiment.

The filtration assembly 110 of the second embodiment comprises a separation chamber 120 having an inlet 121 and an outlet 122 which are misaligned relative to a longitudinal axis of the separation chamber 120, so as to present a convoluted path for the air flow through the chamber 120 (as illustrated with the arrows) to encourage the interaction of the biologically laden aerosol with the charged particles from the first electrode 23 to facilitate the electrostatic charging of the biological matter within the air, and thus to further encourage the precipitation of the charged biological matter upon the second electrode 126. In this embodiment, the separation chamber 120 comprises a cylindrical shape, and the inlet 121 and outlet 122 are separately disposed on an end wall 120a and a side wall 120c respectively of the chamber 120. However, it is to be appreciated that the inlet 121 and outlet 122, may be disposed at angularly and longitudinally separated positions along the curved side wall 120c, such that the air flow is required to change direction within the chamber 120, in passing from the inlet 121 to the outlet 120. In the illustrated embodiment, the inlet 121 is disposed on an end wall 120a of the chamber 120, whereas the outlet 122 comprises an annular aperture formed in the side wall 120c of the chamber 120 and cartridge 150. This change of direction may be further facilitated by the provision of one or more baffles, such as a conically shaped member 160 aligned with a longitudinal axis of the separation chamber 120, which is designed to disrupt the flow of air through the chamber 120 to facilitate electrostatic precipitation. In this embodiment, the conically shaped member 160 extends from the end wall 120b into the chamber, and comprises the moisture absorbing coating 128 for example, disposed on the exterior surface thereof, which is itself covered with the permeable membrane 129.

Upon referring to the illustrated second embodiment of figure 2, the inlet 121 is disposed in a first end wall 120a of the separation chamber 120 and the outlet 122 is disposed in a curved side wall 120c proximate the second end wall 120b of the chamber 120. The first electrode 123 is disposed proximate the inlet 121, similar to the first embodiment, however the second electrode 126 comprises a plurality of concentrically arranged cylindrical members 126a, 126b of which only two are illustrated for clarity, having perforations 126c formed in the curved side walls thereof. Each member 126a, 126b comprises a longitudinal axis which is aligned with a longitudinal axis of the separation chamber 120 and a first end of each member 126a, 126b is fluidly sealed to the first end wall 120a of the chamber 120, around the inlet 121. The second end of each member 126a, 126b is fluidly sealed to the second end wall 120b and the outlet 122 is disposed radially outwardly of the second electrode 126. The perforations 126c within the side wall of each cylindrical member 126a, 126b are angularly misaligned relative to each other, such that the air flow must change direction in passing through the second electrode 126. The air flow is similarly arranged to change direction in moving from the inlet 121 through the second electrode 126 toward the outlet 122. This change in direction encourages an interaction of the charged biological matter within the air flow with the second electrode 126, and thus an electrostatic precipitation thereon.

The means 190 for regulating the air flow speed through the separation chamber 120 of the assembly 110 of the second embodiment comprises a buffer chamber 191 disposed within the air flow path 153 through the assembly 110. The buffer chamber 191 is disposed upstream of the separation chamber 120 and may be further disposed upstream of the cooling unit 130 and heating unit 140. The buffer chamber 191 comprises an inlet 192 which is fluidly coupled with the outlet 301 of a CPAP mask 300 (see figure 3 of the drawings), and the outlet 193 of the buffer chamber 191 is fluidly coupled with the inlet to the cooler/heater unit 130/140 if present or otherwise, fluidly coupled with the inlet 121 to the separation chamber 120.

The buffer chamber 191 comprises a larger internal volume than the separation chamber 120 and is arranged to receive the aerosol, namely the exhaled air prior to passing into the separation chamber 120. The buffer chamber 191 is arranged to present a low pressure chamber to the air flow so that the peak air flow speed through the separation chamber 120 is reduced to a level to facilitate electrostatic precipitation of the viruses and bacteria suspended therein, without substantially increasing the outflow resistance from the CPAP mask 300 (see figure 3 of the drawings). The buffer chamber 191 may be formed of a flexible or distendable material, such as an elastomeric material, so that a volume of the chamber 191 can vary, namely inflate and deflate, with the breathing cycle of an individual for example. In this respect, it is envisaged that the buffer chamber 191 may comprise a bag, for example.

Referring to figure 3 of the drawings, there is illustrated a biological air filtration system 200 according to an embodiment of the present invention, comprising a biological air filtration cartridge 50 having a biological air filtration assembly 10 of the first embodiment disposed therein. However, the skilled reader will recognize that the system may separately incorporate the filtration assembly 110 of the second embodiment within the cartridge 150. The system 200 further comprises a high voltage DC electrical power supply 210, the electrical poles 211, 212 of which are electrically coupled with the first and second connector 24, 27 on the cartridge 50, via a respective wire 213, 214 for example.

During use of the system, the air flow output 301 from a CPAP mask 300 or ventilator is fluidly coupled with the inlet 51 to the cartridge 50 and thus the inlet 21 to the separation chamber 20 via a CPAP hose 302 and hose connector 54 disposed at the inlet 51 of the cartridge 50. The first and second electrical connectors 24, 27 are electrically coupled with the negative 211 and positive pole 212 respectively, of the DC electrical supply 210, and the DC supply 210 is activated to generate an electrical potential difference between the first and second electrode 23, 26 of approximately 4kV- 25kV or more preferably 6kV-15kV. The cooling unit 30 or heating unit 40 is similarly activated to chill or heat the air flowing from the CPAP mask 300 to control the moisture content to reduce the accumulation of moisture within the separation chamber 20. With the DC supply 210 activated, the ion emission zone 23a of the first electrode 23 is arranged to emit electrons therefrom which subsequently attach themselves to the bacteria and viruses (including other detritus including pollen and dust spores, not shown) within the biologically laden aerosol. The electrons generated by the first electrode 23 will drift toward the second electrode 26 by virtue of the electrical gradient established by the potential difference therebetween and thus move with the airflow. The positioning of the ion emission zone 23a proximate the inlet 21 and the reduced air flow speed within the chamber 20 compared with the peak air flow speed within the hose 302 provides a consistently sufficient time for the electrons to interact and attach themselves with the bacteria and viruses within the air flow, prior to passing through the second electrode 26. Accordingly, as the negatively charged biological matter within the air flow passes through the second electrode 26 it will become attracted to the second electrode 26 and deposit thereon. The viricidal coating on the second electrode 26 serves to kill the biological matter in combination with the UV radiation emitting LEDs 60.

The air passing beyond the second electrode 26, namely downstream of the second electrode 26 is thus substantially cleaned of biological matter and is arranged to pass out from the separation chamber 20 through the outlet 22 to the surrounding environment, via a large aperture mesh or gauze 70 which extends across the outlet 22. The mesh or gauze 70 is arranged to prevent unintended access into the chamber 20, and hence any unintended contact with electrodes 23, 26 disposed therein, without establishing a pressure gradient thereacross.

Following a predetermined period of use, or once the colour changing chemical of the moisture absorbing layer 28 indicates that the moisture absorbing layer has reached the absorption capacity, the DC supply 210 is deactivated and the CPAP mask 300 is disconnected from the assembly 10 by disconnecting the hose 302 from the hose connector 54 at the inlet 51 of the cartridge 50. Closures 80, 81 coupled with the inlet 51 and outlet 52 of the cartridge 50 via respective lanyard 80a, 81a are then used to sealing close the inlet 51 and the outlet 52 to prevent the egress of any harmful material therein. The cartridge 50 may then be safely disposed of and a replacement cartridge 50, 150 fitted for further use with a CPAP mask 300, for example.